In a wet clutch system for an automatic transmission, friction plates and reaction plates are typically alternately stacked or interleaved. The friction plates are typically splined at an inner periphery, and the reaction plates are splined at an outer periphery. Accordingly, when the plates are compressed together, frictional engagement between the friction and reaction plates cause the plates to rotate together, thereby transmitting torque between the inner and outer splined interfaces of the plates. The wet clutch is bathed in transmission fluid during operation. This fluid serves as a lubricant as well as a cooling means to dissipate the heat energy formed by actuation of the clutch. The fluid may also contain friction modifiers to increase the effectiveness of the clutch in operation.
As the clutches are engaged and disengaged, a significant amount of heat energy is generated. This heat energy must be dissipated at a sufficient rate to allow the surface temperature of the plates to remain within the working limits of the friction facing layer of the friction plates. The rate of heat dissipation from the plates has an effect on the performance characteristics of the transmission. For example, if the transmission is required to launch a heavily loaded truck traveling up a steep incline, the torque carrying capacity of the wet clutch system must be enhanced. This may be effectuated by increasing the radius of the friction plates thereby increasing the effective friction facing area. However, this increase in radius adds size and cost to the assembly, and may require additional cooling oil to be transferred across the plates for cooling. It may be difficult to keep the center of the larger friction facing layer at an acceptable temperature level since the fluid must migrate from the inner or outer periphery of the friction facing layer toward another periphery.